Improved predictive three-dimensional dose-rate/time/risk models for cancer and systemic injury will be developed for exposure of people to ionizing radiation from internally deposited radionuclides in various organs of the body. These models will be based upon reported experimental studies of internal emitter exposures of laboratory animals (contrasted to available human exposure data). These relationships will also be used to scale from animal data to human risks. The usefulness of such models will depend upon the emphasis to be given for their use for predictive purposes and risk assessment, but an equally important feature will be the underlying biological implications of these models. This project will also develop improved conceptual, biological, and mathematical models based upon theoretical and empirical information for both radiation injury and carcinogenesis. One hit, multihit, multistage, probit, logistic, Weibull, and lognormal radiobiological models will be contrast and compared. Key concepts that will be investigated and evaluated include life- shortening of exposed populations using life-table methods, both stochastic and non-stochastic effects and their inter-relationship, influence of radiation quality factor (Q) with respect to observed relative biological effectiveness (RBE), relative dose-rate effectiveness factor, route and mode of exposure including single acute, repeated or fractionated, and protracted, continuous or chronic modalities involving uniform, increasing, or decreasing dose-rates. Risk assessment will be benefited by the insights that become apparent with these models. The improved conceptualization afforded by them will contribute to planning and evaluating epidemiological analyses and experimental studies.